Sigh. Again you mis-read and attribute thoughts that were not mine. It is never my goal, nor Widom's, to "end up with a mega-relation". She starts with one as a precursor to normalisation
Well maybe my wording was a little clumsy and maybe it is the case that I misunderstand what a mega relation is.
Earlier in this thread you said "finding the FDs is the difficult part"
So when I said "end-up with a mega-relation" , I was intending to say that:
If the FD based normalisation procedure "starts with a mega-relation" ( and it seems that that is the case that we are discussing).
Then: The mega-relation must come from somewhere. It does not just appear out of thin air.
So I was inferring that there must be some previous process that "ends up with a mega relation" to provide the input for the FD analysis process.
In other words, I was asking you describe either your experience or your knowledge of the procedures that others have used to try to understand what steps are required to go from a blank sheet of paper to a paper on which the mega relation is written down such that all concerned say "Yes - that's it! That is the mega-relation. Now you can start the decomposition process."
You did say:
Every FD must be found by experience and intuition, being tested by reference to the business domain.
So I was wondering if you could be a bit more explicit about the steps.
On the other hand, maybe I really do misunderstand the term "mega relation".
What the term brings to my mind is a very large single relation with maybe hundreds of nouns - but maybe that is not it?
You mentioned "Apply(ID,name,campus,sport,HScode,HScity) as being a mega-relation.
If that is indeed the case then I must say that six things in a set of brackets does not seem very "mega" to me.
I thought that the "Apply" relation was just a simple example of the principle rather than a real example of a "mega-relation".
However, if Apply is a mega relation, then it would appear that in any substantial universe of discourse there must be hundreds - (maybe thousands) of such mega relations and when put together they collectively represent the universe of discourse. Which brings me back to my question (slightly modified):
Whether there is just one mega relation or a collection of mega relations, where do the mega-relations come from? By what process are they created?